Fixed missing cases in valid_edge/1.

src/flow_graph.erl

@@ -135,6 +135,7 @@ valid_edge(#edge{from=From, to=To, through=Through}) ->
 	       {hole,      _,          _}        -> IsNeutral(Through);
 	       {#value{},  _,          _}        -> IsNeutral(Through);
 	       {void,      flow,       #value{}} -> true;
+	       {void,      flow,       void}     -> true;
 	       {void,      #dynamic{}, delayed}  -> true;
 	       {void,      _,          _}        -> false;
 	       {split,     #range{},   _}        -> true;
@@ -151,6 +152,8 @@ valid_edge(#edge{from=From, to=To, through=Through}) ->
 		{_,    _,        hole}      -> true;
 		{void, flow,     #value{}}  -> true;
 		{_,    _,        #value{}}  -> false;
+		{void, flow,     void}      -> true;
+		{_,    _,        void}      -> false;
 		{_,    _,        split}     -> true;
 		{_,    #range{}, merge}     -> true;
 		{_,    _,        merge}     -> false;